FOOD. 



213 



water can be supplied as such, the losses of carbon, nitrogen, and oxygen 

 are those to which we should direct our attention in supplying food. 



For the sake of example, we may now take only two elements, carbon 

 and nitrogen, and, if we discover what amount of these is respectively dis- 

 charged in a given time from the body, we shall be in a position to judge 

 what kind of food will most readily and economically replace their loss. 



The quantity of carbon daily lost from the body amounts to about 

 281 '2 grammes or nearly 4,500 grains, "and of nitrogen 18 '8 grammes or 

 nearly 300 grains; and if a man could be fed by these elements, as such, 

 the problem would be a very simple one; a corresponding weight of 

 charcoal, and, allowing for the oxygen in it, of atmospheric air, would be 

 all that is necessary. But an animal can live only upon these elements 

 when they are arranged in a particular manner with others, in the form 

 of an organic compound, as albumen, starch, and the like; and the rela- 

 tive proportion of carbon to nitrogen in either of these compounds alone, 

 is, by no means, the proportion required in the diet of man. Thus, in 

 albumen, the proportion of carbon to nitrogen is only as 3 *5 to 1. If, 

 therefore, a man took into his body, as food, sufficient albumen to supply 

 him with the needful amount of carbon, he would receive more than four 

 times as much nitrogen as he wanted; and if he took only sufficient to 

 supply him with nitrogen, he would be starved for want of carbon. It is 

 plain, therefore, that he should take with the albuminous part of his 

 food, which contains so large a relative amount of nitrogen in proportion 

 to the carbon he needs, substances in which the nitrogen exists in much 

 smaller quantities relatively to the carbon. 



It is therefore evident that the diet must consist of several substances, 

 not of one alone, and we must therefore turn to the available food-stuffs. 

 For the sake of convenience they may be classified as follows: 



A. ORGANIC. 



I. Nitrogenous, consisting of Proteids, e.g. albumen, casein, syn- 



tonin, gluten, legumin and their allies; and Gelatins, which in- 

 clude gelatin, elastin, and chondrin. All of these contain car- 

 bon, hydrogen, oxygen, and nitrogen, and some in addition, 

 phosphorus and sulphur. 



II. Non-Nitrogenous, comprising: 



(1.) Amyloid or saccharine bodies, chemically known as carbo- 

 hydrates, since they contain carbon, hydrogen, and oxygen, with 

 the last two elements in the proportion to form water, i.e., 

 H 2 0. To this class belong starch and sugar. 



(2.) Oils and fats. These contain carbon, hydrogen, and oxy- 

 gen; but the oxygen is less in amount than in the amyloids and 

 saccharine bodies. 



B. IXORGAXIC. 



I. Mineral and saline matter. 



II. Water. 



